The present invention relates to a method for error detection during evaluation of sensor signals, and deals in particular with the evaluation of knock sensor signals in an internal combustion engine.
It is known that during the evaluation of sensor signals which is a basis for the regulation of a technical device, diagnostic measures must be taken which make possible detection of occurring faulty operation of the sensors. Such sensor diagnoses are known in particular in connection with the knock detection and knock regulation in the internal combustion engines. Knock sensors are associated with the cylinders of an internal combustion engine and provide a signal which allows to determine whether an undesirable knocking combustion occurs in at least one of the cylinders. Depending on the informations which are supplied by the knock sensors of the control device of the internal combustion engine, they influence the regulation variables, for example the emission time in the associated cylinders of the internal combustion engine. If a faulty operation of a knock sensor or an associated evaluating circuit is not recognized, there is a danger that the internal combustion engine is operated in an undesirable operational condition, which finally can lead to the situation that the internal combustion engine can be destroyed. Also, a falsly detected error can lead to undesirable operational conditions. For this reason nowadays in all devices for knock emission in internal combustion engine, monitoring measures are performed, which make possible detection of a faulty operation of a knock sensor or an associated evaluating device. A method or an associated arrangement for error detection during a knock detection it is disclosed for example in the patent document PCT/DE94/01041.
From this patent document it is well known that in a device for knock recognition for an internal combustion engine, the initial signals of the knock sensors after a certain preparation for error detection are compared with an upper and a lower rotary speed-dependent limiting value. If the actual standardized reference level formed from the actual sensor signal is located outside of the region formed by these both upper and lower rotary speed-dependent limiting values, an error is detected. A rotary speed-dependent upper limiting value UGO or the rotary speed-dependent lower limiting value UGU are determined so that they are located by a predeterminable fixed amount which represents a safety factor, above or below the possible maximum or minimum standardized reference level at the predetermined rotary speed. The determination of the upper limiting value UGO and the lower limiting value UGU from the maximum or minimum standardized reference level can be performed for example in accordance with plausibility considerations, wherein a once selected dependency of the standardized allowed reference level during the operation of the internal combustion engine is no longer changed. In one embodiment of the known solution, an error is recognized only when the actual standardized reference signal level leaves this region for a predeterminable time and then safety features are introduced which for example maintain an emission angle displacement. The safety features act until the standardized reference level is again located within the permitted region. Under a minimal rotary speed, no diagnosis is carried out.
Accordingly, it is an object of the present invention to provide a method for error detection during an evaluation of sensor signals, in particularly knock sensor signals in an internal combustion engine, in which at least one limiting value is formed in dependence on preceding reference values.
When the method is performed in accordance with the present invention, it has the advantage that a more secure error detection than in the prior art is possible, in which also manufacturing dispersion of the individual sensors as well as the sensitivity of the sensors reduces with time play no role. The safety distance of the rotary speed-dependent upper and lower limiting values from the allowed region of the standardized reference level can be reduced in an advantageous manner, whereby the reliability of the error detection is further increased.
These advantages are provided in that both the upper limiting value and the lower limiting value are designed as self-learning or adaptive-thresholds. These both limiting values or thresholds are rotary-speed dependent and increase with increasing rotary speed. They are dependent in an advantageous manner for preceding values of the standardized reference level and are changeable during the operation, for example of an internal combustion engine. An error detection is performed advantageously only when an actual standardized reference value of the upper limiting value is exceeded by a predetermined factor and/or the lower limiting value is exceeded by a predetermined factor, whereby the factors must not be identical.
In accordance with a further embodiment of the present invention it is advantageous that for the determination of the self-learning or adapted thresholds which form the upper and the lower limiting values of the permissible region, maximal and/or minimal values of the standardized reference level are utilized. These values are stored in suitable storage means of the evaluation device, for example of the control device of the internal combustion engine. This control device, in the case of the knock detection, in addition to the error detection also performs the knock detections and the subsequent knock regulations.
At low rotary speeds, in an advantageous manner a near stronger lower threshold is utilized for the activation of the error detection or diagnosis. Thereby it is guaranteed that in these conditions, no faulty error detection is performed. Also, the minimal rotary speed carried out during a diagnosis is maintained. However, in contrast to the prior art which is disclosed for example in the patent document PCT/DE 94/01041, it is displaced here to small rotary speeds.